There are many situations in industry and in personal safety especially in the construction industry, where a safety element, or strap or tape or cord, is attached either to a person, or to an object. In many cases such safety straps are attached to reels. The reel permits the element to be unwound during normal movement so that the person can move, or object can be moved around in normal circumstances, and to perform normal tasks, without interference. The reel incorporates a rewind mechanism which maintains tension in the element and which rewinds the element into the reel to avoid leaving slack coils or lengths of the element, between the person or object and the reel. Usually the rewind mechanism is in the form of a clock spring which simply uncoils during extension of the element and which rewinds the element as it becomes slack.
In the event however of an emergency caused for example by a slip or fall, or failure of a piece of equipment, then the reel immediately locks to prevent further unwinding of the element, and thus prevents injury or damage. Similar safety element s are in wide use in vehicles, although operated on somewhat different principles.
One of the problems encountered with this type of operation is that, while the reel and element or tape will be operated regularly during normal operating conditions i.e. during safe movement, when the tape or retention cord is unwinding and rewinding slowly, the emergency for which it is designed may only arise, and it is hoped that will only arise, infrequently. Thus the locking mechanism intended to lock up the reel in the event of an emergency operation may be left inactive for months or years at a time.
During this time it may be liable to deterioration due to accumulation of dust, debris, and even rust, depending upon the materials of which it is made. Lubrication if required may have dried out long ago. Maintenance if required may not have been carried out.
One particular situation where a safety element system is required is in a school gymnasium. The gymnasium is usually equipped with basket ball nets. The nets are supported on a pair of parallel arms, in most cases. The arms can be swung upwardly so that the nets are out of the way. During use the arms can be swung downwardly, and the net can be set at various different heights, depending upon the age and skill of the players. These nets are operated by simple hoist systems, in many cases electrically operated hoist systems using a wire rope.
If the hoist fails the entire net and supporting arms can swing downwardly and create a hazard.
Safety regulations require the use of safety element s attached to the net mechanism.
The element s must be free to allow normal swinging of the nets but must stop the net from swinging down if there is a failure of the hoist or wire rope.
One known form of safety element reel is shown in U.S. Pat. No. 4,913,371.
It has a lock mechanism with lock bars 41 which are normally inactive. During normal use the lock bars 41 do not move. The lock bars 41 are intended to swing out and be activated by a sudden abrupt extension movement of the element. In fact the lock bars never move during normal operation of the net.
Over time due to inactivity of the lock bars, there is a possibility that the lock bars might become dusty or clogged and may not function when required.
To overcome this it is preferred that the locking mechanism shall be operated during regular operation of the system.
Preferably the locking apparatus will be such that it is operated repeatedly during normal use, and therefor remains loose and functional so that it is easily operated in the case of an emergency.
Preferably the unwinding of the element and reel will cause repeated operation of the locking mechanism, but in such a way that it does not become locked during normal operation.
When acceleration of the element is smooth and progressive the element can reach a considerable velocity, in the region of 5 ft/sec, before the reel is locked up.
A fundamental advantage of the invention is that the locking mechanism does not remain passive and inoperative, waiting for an emergency to occur, but is in fact operated continuously as the reel unwinds and rewinds, during normal use.
The locking mechanism actively checks the speed of rotation of the reel several times per revolution, the actual frequency being dependent upon the number of detents provided on the reel, as described below. This means that it is virtually impossible for the reel to exceed a safe speed of rotation. The mechanism has a “fail safe” feature, in that if there is a failure of any component the reel will lock.
The system is independent of gravity and can therefore be used in many different orientations without changing its operation.
While reference has particularly been made above to a safety element reel system for basket ball nets it will be appreciated that the invention described below is of much wider application and may be used in the construction of safety retention reels for element s and safety cords, and tapes in many different applications.